Abstract
Abstract. The transform shearing between South American and African plates in the Cretaceous generated a series of sedimentary basins on both plate margins. In this study, we use gravity, aeromagnetic, and resistivity surveys to identify architecture of fault systems and to analyze the evolution of the eastern equatorial margin of Brazil. Our study area is the southern onshore termination of the Potiguar rift, which is an aborted NE-trending rift arm developed during the breakup of Pangea. The basin is located along the NNE margin of South America that faces the main transform zone that separates the North and the South Atlantic. The Potiguar rift is a Neocomian structure located at the intersection of the equatorial and western South Atlantic and is composed of a series of NE-trending horsts and grabens. This study reveals new grabens in the Potiguar rift and indicates that stretching in the southern rift termination created a WNW-trending, 10 km wide, and ~ 40 km long right-lateral strike-slip fault zone. This zone encompasses at least eight depocenters, which are bounded by a left-stepping, en echelon system of NW–SE- to NS-striking normal faults. These depocenters form grabens up to 1200 m deep with a rhomb-shaped geometry, which are filled with rift sedimentary units and capped by postrift sedimentary sequences. The evolution of the rift termination is consistent with the right-lateral shearing of the equatorial margin in the Cretaceous and occurs not only at the rift termination but also as isolated structures away from the main rift. This study indicates that the strike-slip shearing between two plates propagated to the interior of one of these plates, where faults with similar orientation, kinematics, geometry, and timing of the major transform are observed. These faults also influence rift geometry.
Highlights
One-third of the present-day passive margins of the world were formed as transform margins
This type of transform margin was responsible for the generation of the South Atlantic, which was the result of a diachronic breakup between the African and South American plates
Previous studies indicate that the Potiguar rift lies at the intersection of the equatorial margin and the eastern margin of South America and is overburden by the postrift sedimentary units
Summary
One-third of the present-day passive margins of the world were formed as transform margins. Classic models of rifting and lithospheric thinning (McKenzie, 1978) cannot explain the evolution of these transform margins, which are characterized by oblique rifting and often postrift tectonic inversions (e.g., Vagnes et al, 1998) This type of transform margin was responsible for the generation of the South Atlantic, which was the result of a diachronic breakup between the African and South American plates. Rifting in the equatorial Atlantic margin occurred during the early Barremian to Aptian, and the first oceanic crust probably accreted during the late Aptian (Basile et al, 2005) This margin and the associated South Atlantic in the South American plate encompass the Chain, Romanche, and Saint Paul transform faults, which are several hundreds of kilometers long (Fig. 1a). This may have similarities in other basins of the equatorial margin and in other transform margins elsewhere
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